01
The decision is whether to manufacture the next part.
The software result is useful only if it earns a harder test: a reviewed drawing, a manufactured low-risk part, and dimensional inspection.
The full programme asks how agent-assisted mechanical work can remain traceable from requirements through exact geometry, release files, manufactured units, inspection, and corrective action. This checkpoint tests only the transaction from typed operations to an exact model and checked STEP and GLB files.
02
The CAD service owns geometry and history.
The agent selected operations. Schemas rejected malformed calls. OCCT built and checked the solid. Three.js rendered the accepted GLB.
The frozen tool set covered object-neutral primitives, transforms, Boolean operations, holes, slots, fillets, chamfers, measurement, validation, state inspection, and event history. Two neutral preparation runs started empty and ended with the same model and state digests. Their JSON records differ because they retain timestamps and temporary paths; the canonical geometry identifiers agree.
After review, the 12 accepted fixture batches were replayed through the frozen STDIO service from a new empty workspace. The replay reproduced the original model digest, measurements, and byte-identical STEP and GLB files. Its state digest differs because the replay uses new versions, idempotency keys, and event history. The rejected calls were not replayed.
Authority rule
The browser cannot edit geometry. STEP and GLB are derived files. The canonical JSON state, ordered operations, and exact kernel rebuild the accepted model.
03
Version 17 is one checked pre-manufacturing fixture.
The accepted body measures 140 × 90 × 25 mm. OCCT computed its B-rep volume as 138,936.968 mm³.
| Check | Observed result |
|---|---|
| STEP | One solid; less than 0.000001 mm³ floating-point volume delta; 0.001943 mm maximum world-bound delta. |
| GLB | 25 named geometry nodes forming one watertight connected mesh component; 2.117939 mm³ tessellated-volume delta; 0.001943 mm maximum world-bound delta. |
| Artifacts | STEP 96,806 bytes; GLB 170,504 bytes; both bound to V17 by SHA-256. |
04
The rejected calls explain the accepted result.
Schema checks rejected an incorrect box pose, unsupported edge-selector tags, a missing selection distance, and the wrong material field. Exact artifact checks rejected two standalone boss bodies. Applying chamfer after fillets exceeded the STEP bound tolerance by 0.012345 mm, so the intermediate body was removed and rebuilt with chamfer first.
These controls can stop malformed or representation-inconsistent changes. They cannot identify a wrong requirement, unsafe geometry, poor tolerance, unmachinable feature, or bad engineering decision.
05
The next invalidator is physical.
Freeze one drawing, material, process, inspection plan, cost limit, and acceptance rule. Then manufacture and measure the part.
The current record does not test drawings, geometric tolerances, fits, interference, machining rules, structural behaviour, physical material, dimensional inspection, repeatability across tasks, security, or customer value. It also lacks the exact initiating prompt, model identifier, and complete agent transcript, so it is an engineering case rather than a reproducible model evaluation.
The method should be narrowed or stopped if a clean rebuild changes the canonical digests, a new task requires target-specific code, another CAD system cannot read the STEP result inside a declared tolerance, or the manufactured part fails inspection.
06
Primary technical references
- Open CASCADE Technology overview
Exact solid modelling, application data, modification history, and exchange.
- OCCT STEP translator
STEP consistency checks, translation, shapes, topology, and exchange limits.
- CadQuery documentation
Python parametric modelling and high-quality CAD exchange output.
- MCP tool specification
Discoverable tool names, JSON Schema inputs, and structured outputs.
- ISO 10303-242:2025
Managed model-based 3D engineering and the established product-data context for this work.
- NIST downstream model validation
Related work joining STEP product models to manufacturing and coordinate metrology checks.
07
Read Working Paper 02.
The six-page checkpoint records the method, exact values, failures, alternative explanations, cost boundary, invalidators, and next physical test.
Public review draft / not peer reviewed